Conditions InDepth: Brain Tumors

Brain tumors are described differently than tumors found in other parts of the body. A tumor can be benign or malignant. A benign tumor is not cancer and will not spread to other parts of the body. However, a benign tumor can still grow and put pressure on tissue in the brain. This pressure may cause damage to healthy brain tissue and interrupt normal functions of the brain. In certain parts of the brain, this type of pressure can interfere with vital functions, such as breathing or heart rate and cause death.

Malignant tumors grow in an abnormal way and invade tissue around them. Brain tumors rarely spread to other areas of the body, but they can spread throughout the brain. Like benign tumors, damage caused by malignant tumors can cause severe disability and death.

Normal Anatomy and the Development of Brain Tumors

The brain and spinal cord make up the central nervous system (CNS). The CNS affects all of the body, including interpreting sensory information, regulating certain functions like body temperature, digestion, and coordinating physical movements. The brain is also responsible for memory, learning, and emotions.

Certain functions of the brain lie in specific areas. The 3 main areas of the brain and functions that they are responsible for include:

Cerebrum—The cerebrum is the control center for thought, reason, and speech. It processes sensory information from the body and houses the emotional center of the brain. It is divided into 2 large hemispheres, the right and left.

Cerebellum—Found at the back of the head near the base. The cerebellum primarily coordinates movement and balance.

Brain stem—The back and bottom portion of the brain that connects to the spinal cord at the base of the neck. Allows nerves to transmit messages back and forth to the brain. There are 3 parts to the brain stem— the pons, medulla oblongata, and midbrain. These structures control involuntary actions, such as breathing, digestion, and heart function.

Meninges—Three layers of tissue that surround and protect the brain and spinal cord. The meninges lie inside the skull and spine.

Skull—The bony shell that surrounds and protects the brain.

Cerebrospinal fluid (CSF)—Clear, circulating fluid that surrounds, protects, and cushions the brain and spinal cord. CSF can be found inside the meninges.

Blood-brain barrier (BBB)—A barrier that prevents certain substances in circulating blood from getting to the brain tissue. The BBB can keep out harmful substances like infections or toxins, but it can also block medications that may be helpful in treating brain conditions.

Cell division and cell death are a normal process in the body to replace old or damaged cells. Sometimes this division and new cell growth can continue after it is supposed to stop. This excess growth forms a tumor. Benign tumors grow in the area, but do not invade nearby tissue. Malignant tumors are cancer. They grow into nearby tissue. It is not always clear what causes the abnormal growth, but is often a combination of genetic and environmental factors.

Types of Brain Tumors

There are 2 types of brain tumors:

Primary brain tumors start in the brain or in the layers that surround it. It is the second most common type of cancer in children and adolescents.

Secondary brain tumors are tumors that develop because of cancer in other parts of the body. Cancer cells can break from the original site of cancer and travel to the brain in the bloodstream. They are also known as metastatic tumors. Secondary tumors are always malignant.

The location of the tumors will determine the effects and the treatment plan. Most brain tumors are named for the place they start, for example:

Meningiomas—Tumors start in the meninges, layers of tissue that surround the brain and spinal cord.

Gliomas—The glial cells support and protect the neurons of the CNS. There are 3 types of glial cells (astrocytes, oligodendrocytes, ependymal cells) where tumors can start. Astrocytoma is a common type of glioma in adults and children.

Pituitary adenomas—The pituitary is a hormone-secreting endocrine gland located at the base of the brain. Tumors start in the cells of the gland.

Nerve sheath tumors—Neurons are covered in a myelin sheath, which speeds the transmission of messages back and forth to the brain. Nerve sheath tumors may cause loss of the protective sheath, which can affect the function of the neurons.

Medulloblastomas—Tumors that develop in the cerebellum. Though rare in general, it is the most common type of pediatric brain tumor.

Revision Information

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

Overview of intracranial tumors. Merck Professional Version website. Available at: http://www.merckmanuals.com/professional/neurologic-disorders/intracranial-and-spinal-tumors/overview-of-intracranial-tumors. Updated December 2012. Accessed August 13, 2015.